Carbothermal Reduction Process Research Articles

Dual redox electrolytes for improving the performance of asymmetric supercapacitors constructed from heteroatom-doped green carbon spheres

Although supercapacitors benefit from both long-cycle durability and extraordinary power density, unmet energy demands still remain the key challenge on the path of their practical applications. Boosting energy densities without sacrificing the remarkable power densities and long cycle life is of special significance in developing high-performance energy storage systems. Herein, the synergy between reversible redox mediator addition and heteroatom-doping of carbon-based electrode active materials represents an enhanced electrochemical performance of the fabricated energy storage devices. Green carbon spheres (CSs) were synthesized through the eco-benign hydrothermal carbonization (HTC) approach. CSs were then chemically decorated by metal nanoparticles. A carbothermic reduction, in which metallic nano particles nanoparticles played a role as a sacrificial agent, was conducted to prepare highly porous CSs (PCSs). The carbothermic reduction process was followed by heteroatom doping of the PCSs. Nitrogen- and boron-doped PCSs were then utilized as positive and negative electrode active materials, respectively. A combination of potassium iodide (KI) and sodium anthraquinone-2-sulfonic acid (AQSA) was employed as dual-redox mediators to boost the electrochemical performance of the fabricated N-PCS//B-PCS ASC devices. The assembled ASCs coupled with AQSA/KI dual redox additives rendered not only remarkable energy density (86.3 W h kg−1) at a reasonable power density of 340 W kg−1 but also exhibited outstanding cyclic stability (only 22 % decay of initial capacitance observed after 5000 charge/discharge cycle). The encouraging features parallel to the remarkable capacitive performance of the fabricated ASCs make these supercapacitors immensely promising for practical applications.

Silicon from sand is a promising technology for producing silicon of semiconductor quality

An analysis of the methods for obtaining silicon of semiconductor quality determined the relevance of the issues of compliance of modern technologies with environmental requirements of today, as well as the possibilities of raw materials and energy supply for a potential increase in production volumes. The development of production requires a search for compromises between the needs of society and the consequences expressed in the environmental impact on nature, the growth in the consumption of raw materials and energy. The proposal to use quartz sand instead of quartzite is promising due to the solution of the problems of raw material supply for the production of silicon of semiconductor quality for many years to come. The technology of chlorination of quartz sands proposed for implementation has been tested in industrial conditions and, in addition to the problems of raw material supply, to a large extent solves the problems of environmental and energy supply.Within the framework of the set environmental task, the problems of decarbonization of production are first of all solved by eliminating the energy-consuming high-temperature process of carbothermal reduction of silicon. The proposed technological solution provides a compromise between environmental friendliness and energy efficiency by involving silicon-containing materials, technogenic wastes, as “energy donors” in physical and chemical processes. Chlorination of the prepared raw materials is carried out in the solid phase, which is an energy-efficient solution, as it eliminates the cost of energy to compensate for the latent energy of melting. The initial preparation of raw materials involves the procedure of mechanoactivation - energy-efficient activation of the raw material by destroying intercrystalline bonds. The use of “energy donors” in blending ensures that the chlorination process is carried out in the autothermal mode, reducing the specific consumption of chlorine for the process. The problems of high energy intensity in the production of silicon of semiconductor quality are also solved by adjusting the technological scheme with the exclusion of energy-consuming low-temperature processes.The implementation of the proposed technological solutions is focused on the maximum use of known technological equipment, which minimizes the costs of design and production development of the technology. Based on the practical data obtained, system solutions for integrating the new technology into the schemes of existing enterprises are proposed - providing variability of adaptation in terms of raw material supply and the range of produced polycrystalline silicon of both “electronic” and “solar” quality. Based on the practical data obtained, system solutions were proposed for integrating the new technology into the schemes of existing enterprises - providing variability of adaptation in terms of raw material supply and the range of produced polycrystalline silicon of both “electronic” and “solar” quality.

Enhanced removal of metal-cyanide complexes from wastewater by Fe-impregnated biochar: Adsorption performance and removal mechanism

Metal-cyanide complexes are common contaminants in industrial wastewater. Removal of these refractory contaminants is essential before their discharge into the environment. This study investigated a biochar (BC)-based sorbent material that could be applied for the efficient removal of metal-cyanide complexes from wastewater. In consideration of the strong electrostatic repulsion of the pristine BC toward anions, iron-modified BC (Fe-BC) composites were fabricated by a one-step co-pyrolysis of corn straw and FeCl3 at 600–800 °C. The adsorption performance and corresponding sorption mechanisms of representative metal-cyanide complexes (ferricyanide [Fe(CN)6]3- and tetracyanonickelate [Ni(CN)4]2-) onto the Fe-BC composites were investigated. The results indicated that the Fe-BC composites had significantly high affinity toward the metal-cyanide complexes, reaching a maximum sorption capacity of 580.96 mg/g for [Fe(CN)6]3- and 588.86 mg/g for [Ni (CN)4]2-. A mechanistic study revealed that Fe-impregnation during BC fabrication could effectively alter the negatively charged BC surface, forming more functional groups that could interact with the metal-cyanide complexes. Moreover, the transformation of carbon structure promoted the carbothermal reduction process, leading to the formation of various reductive-Fe minerals in the resulting Fe-BC composites. These modification-induced alterations to the surface and structural characteristics of BC were expected to facilitate the adsorption/precipitation of target contaminants. Different sorption mechanisms were proposed for the two metal-cyanide complexes that were the focus of this study. For [Fe(CN)6]3-, precipitation by Fe-bearing species in the Fe-BC composites was the major factor controlling [Fe(CN)6]3- removal, while for [Ni(CN)4]2- hydrogen bonding interactions between surface functional groups (especially hydroxyl (-OH) and carboxyl (-COOH)) and [Ni(CN)4]2- were the main factors controlling removal.

Synthesis of Aluminum Nitride Using Sodium Aluminate as Aluminum Source

At present, the carbothermal reduction and nitridation process is an important method for the large-scale preparation of aluminum nitride powder in industry, but the tremendous energy consumption caused by long-term high temperatures seriously restricts its practical application. To solve this problem, the (NaAlO2+C) mixture with a mole ratio of NaAlO2:C = 1:3 was prepared based on sodium aluminate and carbon black which has been ball milled with anhydrous ethanol as a grinding liquid. The crystal structure evolution and nitridation reaction behavior of sodium aluminate at 800–1600 °C under a nitrogen atmosphere in the presence of carbon were systematically studied employing XRD, SEM, and ICP-MS. The results showed that: high energy θ-Al2O3, η-Al2O3 can be excited by heating sodium aluminate to 1400 °C under a nitrogen atmosphere in the presence of carbon. The transformation process between sodium aluminate and aluminum nitride is carried out via the direct nitridation of θ-Al2O3, η-Al2O3. Benefiting from the direct nitridation of η-Al2O3 and θ-Al2O3, high-purity aluminum nitride powder with a particle size of 0.50 ± 0.18 μm was synthesized at 1400 °C. This work provides a new path for reduced energy consumption in the aluminum nitride industry.

Study on the recovery of phosphorus and iron from molten modified high-phosphorus industrial slag by carbothermal reduction

To effectively recycle phosphorus and iron resources in high-phosphorus industrial slag during molten modification process, the thermodynamic conditions and influence laws of recovery of valuable elements from converter slag with different P2O5 content by carbothermal reduction after melting and modification are systematically analyzed. The results show that the reduction rates of P2O5 and FeO decrease with the increase of P2O5 content at 1450 °C and the basicity of 1.0. Meanwhile, the experimental results prove that the reduction of FeO precedes the reduction of P2O5.The phosphorus element in initial industrial slag mainly exists in the form of Ca5(PO4)2SiO4 and increases with the increase of P2O5 content. With the progress of the carbothermal reduction reaction, the Ca5(PO4)2SiO4 content in experimental slags after reduction decrease significantly. The iron element in initial industrial slag mainly exists in the form of FeO, (MgO)0.239 (FeO)0.761 and Ca2Fe2O5 and disappear after carbothermic reduction reaction. In the range of P2O5 content of 4–8 wt.%, P2O5 content has little effect on the thermodynamic trend of the formation of phosphorus-containing phase Ca5(PO4)2SiO4, but it is not good for the thermodynamic trend of gasification dephosphorization reaction in the carbothermic reduction process. Therefore, the increase of P2O5 content is not conducive to the occurrence of carbothermic reduction gasification dephosphorization reaction.

Terrestrial demonstrator for a low-temperature carbothermal reduction process on lunar regolith simulant: Design and AIV activities

The interest in the Moon exploration and colonization is constantly growing. One of the most critical technologies to be developed to achieve this ambitious goal is the In-Situ Resources Utilisation (ISRU) and extraction. In particular, the water and oxygen extraction from the Lunar Regolith could simplify both manned and unmanned missions, since it can be used for biological purposes or as rocket fuel. To extract oxygen from the regolith, different approaches are under study and development (Schwandt et al., 2012): the most promising are the carbothermal process (Troisi et al., 2022; Gustafson et al., 2010) and the electrochemical reduction (known as FFC Cambridge process (Meurisse et al., 2022)). The paper is focused on the design, manufacturing and testing of the ISRU facility developed at the Department of Aerospace Science and Technologies of the Politecnico di Milano. The plant was realized to demonstrate and validate the carbothermal process for the water extraction from Lunar Regolith simulant, thanks to the activities started under the cap of an ESA study (ESA-E3P-ISRU-SOW-001 –Appendix 1 to AO/1–9183/NL/JK) in a consortium with OHB-I and OHB-S.

Development and investigation of the technological process of plasma carbothermal reduction of slag from secondary metallurgy of aluminum

Based on a critical analysis of the current state and prospects of development of the problem of pyrometallurgical recovery/extraction of aluminum from aluminum-bearing industrial waste, the need to replace traditional, electrocarbonothermic processes and melting process units with innovative, plasma carbothermal processes and furnace-reactors, with the possibility of reverse feeding and recovery of gasified during melting metal and metal oxide components is substantiated. On the basis of this analysis a new technological scheme of smelting with a new design of plasma-arc furnace-reactor, which provides a solution to the problem using a special hollow double-shell graphite cathode connected to the system of circulating supply of gases separated from the reaction zone, was developed and presented. The proposed technological scheme also differs in the use of such highly active liquid and gaseous reagents as carbon-containing reducing agents as calcium carbide (CaC2) and methane (CH4). The main features of chemism of reducing processes are described. It is shown that by replacing traditional coke with anodized calcium carbide and natural gas (methane) the recovery rate of aluminum oxide (Al 29-34%) and silica (SiO2) and hematite (Fe2O3) present with it increases to 80-99%. Specific power consumption is reduced by 35-40%, the 90-95% reduction in the loss of target elements, the 80% reduction in the emission of greenhouse carbon dioxide, which is replaced by a very valuable recyclable synthesis gas - CO-H2. By additionally feeding separate portions of quartzite and steel-rolling scale in the furnace-reactor, a complex alloy-ligature of Fe-Si-Al-Ca system is melted, with the ratio of components: 1:[1.3-2]:[1.3-1.2]:[0.9-1.25]. With the introduction into industrial practice of the plasma carbothermal process of aluminum reduction from secondary aluminum dumping slags accumulated in the world (4 million tons/year), it will be possible to return up to 1-1.5 million tons/year of aluminum to the production processing cycle.

Removal of arsenic, lead and bismuth from copper anode slime by a one-step sustainable vacuum carbothermal reduction process

A green and efficient method for removing arsenic (As), lead (Pb) and bismuth (Bi) from copper anode slime by a one-step vacuum carbothermal reduction process was proposed. In this paper, the Gibbs free energy and saturation vapor pressure for the reduction process were analyzed theoretically. The effects of temperature and holding time on the reduction and removal ratios for As, Pb and Bi were investigated experimentally. The results showed that the weight loss ratio of the feedstock was 48.28 %, and Pb and Bi decreased to levels below the lower limits for detection with inductively coupled plasma atomic emission spectrometry (ICP–AES), i.e., from 4.81 % and 7.32 %; these values were determined for the optimal vacuum carbothermal reduction conditions, which included a reaction temperature of 1073 K, a holding time of 2 h and a system pressure of 10 Pa. 81.81 % of the As and all of the Pb and Bi were removed. The amounts of Ag and Au recovered in the residue increased from 10.64 % and 510 (g/t) to 15.61 % and 742 (g/t), and the recovery efficiencies were 99.76 % and 99.9 %, respectively. The innovative process proposed in this paper thoroughly separated As, Pb, Bi and precious metals. Volatiles such as As2O3, PbS, and BiSe were placed in lead smelting plants, and the Ag and Au in the residue were placed in copper anode slime for extraction of precious metals, which greatly improved the efficiencies for recovering valuable metals from anode slime and avoided emission of arsenic-containing waste gas and wastewater.

Rational design of AgCl@Zr3+-ZrO2 nanostructures for ultra-efficient visible-light photodegradation of emerging pollutants

Achieving high-efficiency charge separation and strong oxidizing capacity are of great significance for photodegradation of organic pollutants. Herein, novel self-doped Zr3+-ZrO2 nanoclusters and AgCl@Zr3+-ZrO2 heterostructures with high surface areas were fabricated for photodegradation of organic pollutants under visible-light illumination. The experimental results revealed that self-doped Zr3+-ZrO2 clusters were formed during a carbothermal reduction process, and the adsorbed surface chlorine promoted the adhesions of Ag+ to form AgCl over the surface of Zr3+-ZrO2 clusters. The obtained AgCl@Zr3+-ZrO2 heterojunctions displayed ultrahigh-performance degradation of norfloxacin under visible-light illumination, and the prepared AgCl@Zr3+-ZrO2-11 heterojunction presented the highest photocatalytic performance with a rate constant of 0.21989 min−1, which was approximately 62.12 times that of Zr3+-ZrO2 clusters and 21.95 times that of AgCl and far better than that of commercial ZrO2. The formation of Zr3+ self-doping, strongly combined interfaces, and high surface areas highly promoted charge separation for highly enhanced photodegradation of organic pollutants.

Kinetic study in selective reduction of limonitic and saprolitic nickel ore

ABSTRACT Saprolite and limonite have different behaviour in the carbothermic reduction process due to the differences in their atomic structures. This work investigates the kinetic study of these two different kinds of lateritic nickel ores. Nickel ore, coal, sodium sulfate, and calcium oxide were mixed, then pelletised into 10–15 mm diameters. The pellets were reduced with a non-isothermal condition using a muffle furnace at 950–1150 °C for 5–120 min. The reduced pellets were crushed into less than 74 µm prior to the wet magnetic separation process to obtain concentrates (ferronickel) and tailings (impurities). The result showed that the reduction rate for both lateritic nickel ores increased with the increase of reduction temperature and holding time. The Ginstling-Brouhnstein model was appropriate to describe the diffusion mechanism of the reduction process of limonite and saprolite. The activation energy in the reduction of limonite was lower than in saprolite. It indicated that the iron and nickel in magnesium silicate in saprolite have lower reducibility than the oxide structure in limonite. Modifying basicity in nickel laterite with CaO addition could also reduce the activation energy.

Pyrolytic synthesis and performance efficacy comparison of biochar-supported nanoscale zero-valent iron on soil polluted with toxic metals

ABSTRACT Toxic and hazardous metals such as cadmium (Cd) and Lead (Pb) can cause cancer in humans; hence, reducing their bioavailability in the soil is crucial for human health and environmental safety. In this study, biochar modified with nanoscale zero-valent iron (nZVI-BC) was synthesized from low-cost adsorbent waste materials and iron (iii) oxide (Fe2O3) via carbothermal reduction process for stabilization of Pb and Cd in the soil. Furthermore, an evaluation of treatment efficiency on exposure health hazards for both carcinogenic and non-carcinogenic risks was done. The results revealed that nZVI-modified eggshell biochar was able to reduce the concentration bioavailable of Pb and Cd in soil by (69–75%) and (62–65%), and reduce the toxicity leaching of Pb and Cd by (53–66%) and (68–75%), respectively. The treatments reduced carcinogenic risk (CR) and hazard index (HI) in children and adults by 35–47% for Pb and 25–36% for Cd, respectively. Hence, this study proposes a new way to reduce and modify environmental wastes to make nZVI-supported biochar that can remediate toxic metals from the soil, improve soil nutrients, reduce human exposure health risks, and enhance the environment’s health.

Synergistic strengthening mechanisms of mechanical activation-microwave reduction for selective lithium extraction from spent lithium batteries

Carbothermal reduction of cathode materials is an effective method to selectively extract lithium carbonate, both mechanical activation and microwave heating can enhance thermal reduction of mixed electrode materials. However, the mechanism of enhanced lithium extraction has not been fully revealed. This study attempts to uncover the synergistic strengthening mechanisms of mechanical activation-microwave reduction from the aspects of material structure, dielectric properties, reduction kinetics and lithium recovery rate. Mechanical activation induces amorphization and structural defects. The enhanced dielectric properties of materials and the induced hotspots/arc plasmas are also responsible for the enhancement of the reduction reaction. The average dissociation activation energy in the activated sample is 18.0 kJ·mol−1, which is 20.3 kJ·mol−1 lower than that of unactivated sample. The model-free method reveals that the carbothermic reduction process can be divided into three stages: (I) initial stage (α < 0.4(0.6)): the activation energy gradually decreases with the formation of strong microwave acceptor-reduction products; (II) transitional stage (0.4(0.6) < α < 0.7): the increase in mass transfer resistance leads to gradual increase in activation energy. Mechanical activation shortens the transitional reaction stage; (III) later reaction stage (α > 0.7), the decrease in activation energy may be attributed to the enhanced microwave absorption and CO reduction. The model-fitting method reveals that after mechanical activation, the reaction kinetic changes from reaction-order model to Ginstling-Brounshtein diffusion model. The optimized lithium extraction process parameters were: activation 300 rpm for 1.5 h, reduction temperature 550 °C. The research results can provide theoretical support for the enhanced extraction of cathode materials.

Effect of Inner Reductant Addition and Laying on Carbothermic Reduction Process of Laterite Nickel Ore/Coal Composite Briquette

Effect of Inner Reductant Addition and Laying on Carbothermic Reduction Process of Laterite Nickel Ore/Coal Composite Briquette

A clean and efficient utilization of fly ash with a focus on the strengthening decomposition mechanism of mullite

A novel method of comprehensive disposal of low temperature and high-efficiency reduction of fly ash to produce ferrosilicon without slag under the action of Fe2O3 was proposed in this paper. In addition, the promotion of Fe2O3 on the reduction and decomposition of fly ash at a low temperature and the strengthening mechanism of the reduction and decomposition of the mullite phase were systematically studied. The thermodynamic analysis shows that the decomposition reaction of mullite can be carried out only after the free SiO2 in fly ash is exhausted. Combined with the thermodynamic prediction of the equilibrium phase concentration of reduction products, the phase evolution of reduction products and the results of SEM microanalysis, it is proposed that the carbothermal reduction process of fly ash and the decomposition mechanism of mullite are as follows: iron oxide reduction, mullite decomposition into aluminum–silicon oxide and aluminum–silicon oxide deep decomposition and complete release of Al2O3, while the final products of reduction decomposition are ferrosilicon phase and alumina. According to the mineralogical characteristics of reduction decomposition products, a novel idea of preparing ferrosilicon and alumina/calcium aluminate byproducts by electric furnace melting is proposed, which lays a theoretical foundation for the large-scale, slag-free and high-value utilization of fly ash.

Multifunctional ultralight, recoverable, piezoresistive, and super thermal insulating SiC nanowire sponges

AbstractUltralight three‐dimensional (3D) architectured silicon carbide (SiC) nanowire sponges with integrated properties of recoverable compressibility, outstanding high‐temperature thermal and chemical stability, and fire‐retardance have been actively pursued in recent years. However, efficient construction of SiC nanowire sponges with well‐controlled overall shapes and distribution of SiC nanowires remains challenging. Herein, by coupling the electrospinning technique and carbothermal reduction process, we have developed a new fabrication process for highly porous and free‐standing 3D SiC nanowire (SiCNW) sponges with closely attached nanowires through thermal treatment of stacked electrospun PAN/SiO2 nanofiber membranes. The resulting SiCNW sponges possess ultralow density (∼29 mg cm−3), excellent compressive recoverability from large compressive deformation (up to 40% strain), and fatigue resistance, which endow them with excellent piezoresistive sensing capability under a variety of complex conditions. Furthermore, the sponges display superb thermal insulation (thermal conductivity of 24 mW m−1K−1) and fire‐retardance. We believe that the present process provides technical clues for the development of other multifunctional ceramic sponges, and that further development of these ultralight multifunctional ceramic sponges offers potential for the design of advanced components for application in harsh engineering environments.

High performance LiFePO4 nanomaterial obtained by a tavorite-to-olivine phase transition at low-temperature

The main problem currently faced in the large-scale production of LiFePO4 by solid-phase methods is the high energy consumption caused by solid/melt-phase lithiation process. Herein, LiFePO4 nanoparticles are successfully obtained by a phase transition from the tavorite LiFePO4OH structure to the olivine LiFePO4 structure at low-temperature (550–600 °C). This desirable LiFePO4OH precursor is prepared via a wet pre-lithiation process, and its thermodynamic feasibility is demonstrated by thermodynamic calculation. The liquid-phase lithiation followed by a simple carbothermal reduction process (c.f., the solid/melt-phase lithiation process of the traditional solid-state method) results in a superior mass transfer efficiency and reaction uniformity. It therefore prevents the requirement for a higher temperature and longer sintering process. It is also indicated that on the premise of the lattice perfection, a lower crystallization temperature is not only conducive to widening the effective ion diffusion channels of LFP, inhibiting further crystal growth, and shortening the diffusion path, but it also reduces the synthetic cost. As a result, a crystallization temperature of 600 °C (or 550 °C) is optimal, and the resulting LiFePO4 electrode can deliver an appealing high rate capacity of 147.7 mA h g−1 at 10 C. It is expected that this novel synthetic route could be employed for the large-scale commercial production of high performance LiFePO4 cathode materials at a low cost.

Discovery of terrestrial andreyivanovite, FeCrP, and the effect of Cr and V substitution on the low-pressure barringerite-allabogdanite transition

Abstract Iron phosphides with significant variations of Cr (up to 18 wt%) and V (up to 8.6 wt%) contents were detected in gehlenite-bearing breccia at the Hatrurim Complex, Negev desert, Israel. Investigations of the composition and structure of the Fe2P phosphides showed that when the V+Cr content is higher than 0.26 apfu (atoms per formula unit), a transition from the hexagonal barringerite (P62m) to orthorhombic allabogdanite (Pnma) takes place. According to the experimental data, allabogdanite is a high-pressure (&amp;gt;8 GPa) polymorph of barringerite. Pseudowollastonite associated with Cr-V-bearing allabogdanite is an indicator of phosphide crystallization at high temperature (&amp;gt;1200 °C) and low pressure. Thus, at the low pressure close to ambient, when more than 13 at% Fe in Fe2P is substituted by Cr and V, the ortho-rhombic polymorph is stable. The orthorhombic phosphide with the highest Cr and V contents belongs to the andreyivanovite species with the FeCrP end-member formula. This is the first finding on Earth of that very rare mineral described from the Kaidun meteorite. Some Cr-V-bearing phosphides have an unusual morphology, which cannot be explained by crystallization from a melt. More probably, these phosphides can form in the process of replacing fish bone remains. We believe that sedimentary protolith was not thermally altered and contained a significant amount of bituminous organic matter and phosphorite inclusions. Injecting paralava into the sedimentary rocks determines the conditions for phosphide formation on the boundary of these rocks as a result of the high-temperature carbothermal reduction process.

Thermoelectric properties of oxygen-deficient spinel-type ZnxFe3−xO4−δ prepared by carbothermal reduction and spark plasma sintering

This paper describes the effect of oxygen vacancies, which are induced by a carbothermal reduction process and spark plasma sintering (SPS) treatment, on the thermoelectric properties of spinel-structured zinc ferrites ZnxFe3−xO4 (0.2 ≤ x ≤ 1.0). Characterization of the oxygen-deficient ZnxFe3−xO4−δ materials revealed that Zn2+ preferentially occupy the octahedral B-sites and that valence modification of Fe3+ to Fe2+ occurred, resulting in an excess of n-type carriers at B-sites and an increased power factor. In addition, Co substitution enhanced the power factor for the materials over the entire investigated temperature range. Compared with the carbothermal reduction process, SPS treatment effectively introduced oxygen vacancies within a short time and resulted in a material with a substantially improved electrical conductivity.

Viscosity and structure evolution of molten vanadium slag during carbothermic reduction process

In this study, the viscosity and structure evolution of molten vanadium slag at different stages during carbothermic reduction process were investigated through employing the rotating cylinder technique, Fourier transformation infrared (FTIR) and Raman spectroscopy. The results showed that both the viscosity and apparent activation energy of the slag continuously increased with the decrease of FeO and MnO contents, while decreased with the decrement of Cr2O3 and V2O3 contents. The mole fractions of Q2 and Q3 units in the silicate melt increased significantly due to the decrease in the concentration of free oxygen with the reduction of FeO and MnO, and the structural units transformed from prevalent Q0 and Q1 to Q2 and Q3 dominant, resulting in the fact that the trough depth of the [SiO4]-tetrahedral band was obviously enhanced and its center shifted to a higher wavenumber region in the FTIR spectroscopy. On the contrary, the reduction of Cr2O3 and V2O3 brought a gradual increasing Q0 and Q1 concentration and lower polymerization degree of molten slag, while the trough depth of the [SiO4]-tetrahedral band was weakened and its center shifted to a lower wavenumber region, which responded well to the viscosity variation of the slag.

Double-Enhanced Core-Shell-Shell Sb2S3/Sb@TiO2@C Nanorod Composites for Lithium- and Sodium-Ion Batteries.

For most alloying- and conversion-type anode materials, a huge volume expansion and structure degradation of the electrodes always hinder their applications. In this work, a novel core-shell-shell Sb2S3/Sb@TiO2@C nanorod composite has been designed layer by layer, which includes an inner Sb2S3/Sb heterostructure core protected by an oxygen-deficient TiO2 shell and a conductive carbon shell. It is interesting to observe that, during the carbothermic reduction process, the previous Sb2S3 nanorod cores are partially reduced into a metallic Sb phase and the reduced TiO2 also creates many oxygen vacancies, which can greatly enhance the conductivity of the semiconductor Sb2S3. Thanks to the double effects of the TiO2 middle shell and carbon outer shell, the unique double-shelled structure design creates an enhanced dual protection, which can better accommodate the volume-expansive deformation and preserve the structural integrity of the active Sb2S3/Sb core. Especially, the TiO2 middle layer is self-assembled by numerous nanoparticles acting as a nanopillar backbone, which supports between the nanorod core and outer carbon shell to better buffer the volume changes. As a result, the core-shell-shell Sb2S3/Sb@TiO2@C anode shows lithium and sodium storage performances superior to those of the pristine Sb2S3 and core-shell Sb2S3@TiO2 electrodes. For lithium-ion batteries, the Sb2S3/Sb@TiO2@C nanorod composite achieves an initial discharge/recharge capacity of 1244.9/1005.1 mAh g-1 with an initial Coulombic efficiency of about 80.7%, an enhanced rate capability with a capacity of 593.2 mA h g-1 at 5.0 A g-1, and prolonged cycling life for 500 cycles with a reversible capacity of 495.8 mAh g-1 at 0.5 A g-1. For sodium-ion batteries, the nanorodalso exhibits an improved performance with an initial discharge/recharge capacity of 781.4/574.0 mAh g-1 (initial Coulombic efficiency of about 73.46%) and cycling for 400 cycles with a reversible capacity of 422.6 mAh g-1 at 0.8 A g-1. This research sheds light upon double-shell structure designs with an effective middle shell to enhance the energy storage performance of electrode materials.